The list of best practices are as follows:

1. Engage Quickly - (my interpretation: provide value within 30 seconds)
2. Mimic Look and Feel - (make your widget look like the page it is in)
3. Enable Self Expression - (let people personalize their widgets)
4. Make it Dynamic - (keep showing new stuff)
5. Expose Friend Activity - (show what friends are doing)
6. Browse the Graph - (let people explore their friends and friends of friends)
7. Drive Communication - (provide commenting features)
8. Build Communities - (expose different axes of similarity)
9. Solve Real World Tasks - (leverage people’s social connections to solve real problems)